1. Field
The present general inventive concept relates to a power supplier to supply power through a switching mode operation, and an image forming apparatus including the power supplier, and more particularly, to a power supplier capable of increasing in-use safety and product reliability, and an image forming apparatus including the power supplier.
2. Description of the Related Art
Generally, a power supplier to supply power is required to operate an electronic device. Recently, a switch mode power supply (SMPS) that provides a stable direct current (DC) output voltage by controlling a current flowing through an inductor by using a pulse-width modulated signal has been used in electronic products.
The SMPS uses a semiconductor device, such as a metal oxide semiconductor filed effect transistor (MOSFET) for power, as a switch, and controls the current flowing through the inductor by using the switch so as to output a DC output voltage having any one of various values. The SMPS is widely used since the SMPS has high power converting efficiency compared to a conventional linear power supplier and has a small volume, by controlling switching of the semiconductor device.
FIG. 1 is a diagram of a general power supplier 100.
Referring to the power supplier 100 of FIG. 1, a capacitor 125 is charged by using a predetermined voltage supplied through a power supply (V1) 110.
As a predetermined voltage of a DC component is charged in the capacitor 125, a predetermined voltage is trapped between a first node N1 and a second node N2. Hereinafter, a voltage trapped at both terminals of the capacitor 125 is denoted by Vc. Also, a Voltage Vc is trapped at both terminals of a first inductor 131.
When a switching device 132 is turned on, a transformer including the first inductor 131 and a second inductor 133 transforms a voltage at both terminals of the first inductor 131 and transmits the transformed voltage to the second inductor 133. A transformation ratio varies according to turn ratios of the first and second inductors 131 and 133.
A first controller 140 outputs a switching control signal to control an on or off position of the switching device 132. In FIG. 1, a MOS transistor is used as the switching device 132, and the switching control signal is applied to a third node N3 constituting a gate terminal of the switching device 132.
When the switching control signal turns on the switching device 132, a current flows through the first inductor 131, thereby generating an induced current in the second inductor 133, and thus a predetermined voltage is trapped at both terminals of the second inductor 133. Also, a current flowing through the second inductor 133 is rectified through a diode 151 and is supplied to a fourth node N4 constituting an output terminal. Also, a load 160 having a predetermined value may be connected to the fourth node N4.
According to the energy related international standard, standby power of an electronic product including a power supplier is limited to 0.5 W or below. Thus, manufacturers of an SMPS reduce power consumption of devices consuming power, such as a discharge resistor and a dummy load, in the SMPS.
However, when loads of the discharge resistor, the dummy load, etc. in the SMPS are reduced, a discharge time of the capacitor 125 is increased, and thus an error may be generated during rebooting. Further, even if the SMPS is turned off, a user may get an electric shock due to a voltage left in the capacitor 125.
Here, the discharge time denotes time taken from a point of time when supply of power applied to the capacitor 125 is blocked to a point of time when a voltage trapped at both terminals of the capacitor 125 is decreased to a predetermined voltage or lower.
For example, even if the power supply 110 is blocked to repair the SMPS or the like, a voltage remains in the capacitor 125. Thus, when the user contacts the capacitor 125, the user may get an electric shock or be burned due to the electric shock.